If I remember correctly, when you fire 2 guns beside each other at the exact same time, the pressure from the gases expelled when fired from each barrel will have a small effect on the direction of the shells, causing inaccuracy. A minor issues are very close ranges, but as range increases, the inaccuracy becomes a problem.

Yeah, this thread showcases some of the common misconceptions about battleships. While some of the WW1 designs might have been full of fail or bad designs in general, everything afloat in WW2 pretty much adheres to the following truisms.

1 - A ship does not move when it fires it's guns, even a full broadside. Battleships (and battlecruisers) were designed first and foremost as stable firing platforms. The entire reason the ship exists is to get those 6 to 12 rifles into combat, and keep them there. Between recoil absorption in the gun carriage and the awesome mass of the ship itself... the ship does not move when the guns are fired. Doing so would be a total engineering fail.

2 - That said, a ship fires only a few barrels at once for other reasons... usually targeting. Standard procedure to begin a surface engagement was to fire each barrel at a slightly different angle and observe the shot fall around the target, then adjust subsequent firings to improve accuracy. Once shots begin landing on target, more gun barrels are fired simultaneously.

2A - Modern video of fire support from US Battleships often shows single-barrel firing. This is because the video is commonly shot during gun training, when simultaneous fire is not required, or during live fire on land targets, where usually only 1-2 shells per target are required.

3 - Guns fired simultaneously do not mess up the trajectories of the shells fired. Gas expansion and turbulence is a problem, but not for the shells fired at exactly the same time, as the projectiles are in FRONT of the disrupting gas expansions. Now a turret that fires guns one barrel at a time DOES have to wait a short time between firings so hot gas dissipates between firings, but the time delay is under 1 second, so it's not usually an issue for any ship using electronic fire control from a central gun commander position. (Older ships whose gun crews fired the guns manually on orders DID sometimes suffer from gas expansion inaccuracy.)

gas expansion cause some trouble for crews manning exposed AA guns and tended to give them concussion but I don't think this affected full salvo firing practice.

I think this thread goes some way to dispel some myths about BBs as someone else already said.

IJN Mogami had structural issues but that's because the Japanese were trying to cheat treaty limits and put far too many guns on it. As a counter-example, USS Iowa fired her guns for over 60 years without concern for structural damage. WW2 BBs were designed to take torpedo shock damage (and some did without sinking) so I don't see how the gun recoil is comparable. Sure a broadside looks impressive, but actually the force transferred to the structure is not very large in the majority of well-designed ships.

As for interference, this partly due to the fact there is small variance in muzzle velocity so sometimes shells would overtake each-other in flight, and the wake of the one in front would upset the others hence giving worse spread.

The actual effect of all this on spread is probably minor, but it's one of those things people pick on.

The USN claimed to have these problems with their treaty cruisers (Northampton-Portland) as the barrels were very close to each other in the turrets and could only elevate together (done to save space and weight). Note how the Baltimore class has wider spaced barrels on the turret and they can all elevate individually.

Iowa-class had electronic timers that offset the firing of guns from the same turret so there would be enough delay between the shells to avoid interference.

lol, cute but not really accurate. The ww1 & 2 fire in gradual for 2 purpose, splash observatory and accuracy. take revenge class, 4 turrets, one turret fire and observer see where the shells lands by looking the splash, after readjusting distance over wind factor and gun angle, the other guns then adjusted (already loaded) and then begin second shots to sink the enemy vassel. in ww2, german make sheetak (spelling?) radar that improve long range gunnery and observation scout planes equip with radio making shot fired more accurate.

rodney & nelson can fire a full broadside without suffering breaking, even the heavily armed agincourt (sultan selim 2) with 7x2 12inch gun can fire a full broadside at once with 'awe feeling'. most of the time they fire full broadside when demonstration, testfire and coastal bombardment.

for more info, search for the function of salvo, firing barrel by barrel give time to the other gun to reload, thus giving the impression of non stop firing from a ship with devastating morale and physical damage

OK first thing first...

Not all ships fired in gradual mode during WW2.

Bismarck used a german approach in battle ( no, im not kidding, a german ship using a german approach heh).

This ment fiering turret A(nton) first (2 barrels at the same time) and waiting for hits/splashes. Firecontrol would then suggest changes in aiming for turret B(runo), which would than fire and this process would be repeated with all turrets untill a proper fiering solution was gained.

When first hit would be scored, then fiering officer would either order partial (2 turrets at a time) or full salvos (all turrets at the same time.

http://www.kbismarck.com/controltiri.html

On the allied side they had a totally different approach. Going from WW1 experiance, british fired full salvos constantly thinking that "more shells in the air, bigger the chanse of a hit + enemy is under bigger psyhological pressure".

Gradual firing of barrel per barrel originates from "modern" days. When Iowas were first modernized with computers, it was found out in trials that full broadsides crash most of sensitive computers and harm the sophisticated equipment then installed in general and full slavos also cause major stress to ships hull. Thats why they dont use full broadsides anymore.

BTW Bismarcks (and those of tirpitz) turrets had barrels far away from each other to minimize the shaking effects and disturbancess of one on another. No matter how close it seems to a human eye, no shell is fired simultaniously as another so it affects accuracy to a little extent. Afcourse that extent means something when a shell travels a long distance. Thats why gradual is also better.

Now second. Rodney wasnt seriously damaged by firing its own guns. She was sheduled for maintance even before the engagement with Bismarck. If some crewmen couldnt take a dump cause a toilet was broken resulting from own gun blast damage.... that shouldnt be taken as having an effect on combat ability. :D

Third. Ships dont move in water because of recoil, at least not sideways. The excesive recoil, that is not absorbed by gun-recoil dampners resultes in a ship rolling a bit. And that stops almost instantly.

Also I suppose since all gun had her crew working and operating the gun independently, they shot when they could.

Iowa-class could fire independantly each guns of each turret.